Control apparatus



Oct. l2? 1943. G. P. MARcY 2,331.408

CONTROL APPARATUS Filed Jan. 18, 1941 2 Sheets-Sheet l Y 71mm?wlTNEssE's: iNvENToR d GERSLLCY ATTORNEZ Oath/12,' a Il. MARCY l2,331,403

CONTROL APPARATUS Filed Jan. 18. 1941 2 Shouf-Shoot 2 INVENToR GERALD P.MARcY.

`ATToR Y Patented Oct. 12, 1943 coN'rnor. APPARATUS Gerald P. Marcy,Longmeadow, Mass., assignor to Westinghouse Electric & ManufacturingCompany, East Pittsburgh, Pa., a corporation of Pennsylvania ApplicationJanuary 18,: 1941, Serial No. 374,997

(Cl. 20o- 139) 7 Claims.

This invention relates to control apparatus and more especially tothermostatically-controlled switches adapted for use in refrigeratingapparatus.

'I'hermostatic switches adapted for controlling electric circuits whichinclude an inductive load require a snap-acting opening movement of theswitch to prevent excessive arcing. A certain amount of power isrequired to actuate the snapacting device associated'with such switcheswhich power is generated by the temperaturercspon sive element passingthrough a certain temperature range. This temperature range is known asthe temperaturediilerential of the thermostatic` switch. It is usuallydesirable to have the temperature differential as small as possible inorder to maintain the temperature of the media being controlled withinclose limits. This, heretofore, either required a largetemperature-responsive element `or a delicate snap-acting mechanism,both of which are expensive.

It is accordingly an object of the invention to provide a snap-actingthermostatically-controlled switch which operates on a 'smalltemperature differential and is of simple and rugged construction.

Another object of the invention is to provide novel means for lockingthe thermostaticallycontrolled contacts in the open and closed`position.

These and other objects are effected by my invention as will be apparentfrom thf` following description and claims taken in connection with theaccompanying drawings, forming a part of this application, in which:

Fig. l is a section of the thermostatic` switch of this invention, thecontacts being shown in the closed position by the lfull lines and shown-locked in the closed position by the dotted lines;

Fig. 2 is a section of the thermostatic switch ofv thermostatic controlswitch, designated by numeral 3, embodies a cup-shaped container I0, the

disc I2 rests. The bimetallic disc I2 is slightly dished to provide asnap-acting movement of the central portion thereof, the movement beingdownwardly when the temperature increases above a predetermined point.The disc tends to Snap upwardly when the temperature decreases belowsaid predetermined point by an amount equal to the temperaturedifferential'of 'the disc. The central portion of the disc I2 isprovided with an opening I3 through which upper portion I4 of anactuating 'rod I5 extends, which portion I4 is threaded and secured inthe opening I3 by a necked nut I6 and by alock nut IE.

The disc I2 is retained on the shoulders I I by a generally U-shapedspring I8, one end oi which is secured by a rivet I9 to an indentedportion 20 in the lip of the cup IIl. The cup is closed by a cover 2|having a central opening 22 through which the threaded shaft 23 of anadjusting screw 21 extends. The threads of the shaft 23 engage thethreads of a nut 24 secured to the top wall of the cover 2l adjacent theopening 22. The lower end of .the shaft 23 bears against one end of thespring I8 and is located directly above the actuating rod I.

The function of the spring I8 is to vary the temperature characteristicsof the bimetallic disc I2. An increase in the pressure of the spring I8on the upper portion of the actuating rod I4, such as may be effected byscrewing the adjusting screw 21 downwardly reacts on the disc 2|,causing it to snap upwardly or downwardly at a lower temperature thanformerly.

this invention with the contacts in the open-.

position;

Fig. 3 is a section of the thermostatic switch showing the contactslocked in the open position;

Fig. 4 is a sectional view on the line IV--IV of Figi;

Fig. 5 is a plan view of the thermostatic switch with the cover removed;

Fig. 6 is a sectional view on the line VI-VI of Fig. l; and

Fig. 7 is a view of the thermostatic switch of this invention installedin a domestic refrigerator to control the refrigerating apparatusthereof,l

the bottom of the refrigerator being broken away. Referring vnow to thedrawings in detail, a

The, actuating rod I5 comprises a central portion 25 of insulatingmaterial, and a lower portion 26 of metal on whichtwo spaced-apartcollars 28 and 29 are formed. Both the upper portion I4 and the lowerportion 26 are rigidly .ie-

cured to the central portion25 by a mortise and pin joint. The lowerportion 26 of the actuating rod I5 passes through a central opening 3|of a bimetallic strip 32, which strip is clamped between the collar 28and a ring 33 pressed on the shaft. The bimetallic strip 32 is adaptedto flex upwardly at its center when heated.

An electric contact button 34 is affixed to each end of the bimetallicstrip 32 and said contact buttons 34, respectively, engage a second pairof contact buttons 36 secured in, but insulated from the base of the cupI0 Vand in electrical connection with insulated lugs 35 on the outerside of the casing III. The contacts 34 are maintained in a positionabove the contacts 36 by guides 31 of insulating material adjacent theends of the bimetallic strip 32. The upward travel of the actuating rodI5 is limited by stops 38 projecting inwardly from a U-shaped section ofmolded electrical insulating material 39 secured by rivets 4I to thebase of the cup I which stops 38 engage the lower collar 29. As shown inFig. 1, the biinetallic disc I2 closes the contacts 34 and 36 when thedisc I2 snaps downwardly and, as shown in Fig. 2, opens them when thedisc I2 snaps upwardly.

When the adjusting screw 21`is turned downwardly to the point where thefreeend of the spring I8 touches the portion of said spring I8immediately below it, the contacts 31 are forced to and locked in theclosed position against contacts 36. This position is illustrated by thedotted lines of Fig. 1. The U-shaped configuration of the spring I8 thusaffords a resilient body between the shaft 23 of the thumb screw 21 'andthe operating rod I for a limited displacement which body thereafterbecomes rigid.

The adjusting screw 21 also provides for forcibly opening the contacts34, 36. As shown in Fig. 3, the upper edges 43 of the U-shapedinsulating material 39 engage the bimetallic strip 32 at two points onopposite sides of the actuating rod I5 and between the contacts 34 whenthe adjusting screw 21 is screwed down to'a position beyond that sli-ownby the dotted lines of Fig. 1. The bimetallic strip 32 is flexible sothat forcing the actuating rod I5 downward causes the portion of thestrip 32 which lies between the two upper edges 43 of the insulatingmaterial to bend downwardly. This downward bending causes the ends ofthe strip 32 to pivot on the upper edges 43 of the insulating material39 and raise the ends of the strip 32 and the contacts 34 thereon. Thisaction separates the contacts 34 from the contacts 36.

The control of this invention is adapted to tion in such apparatus isshown in Fig. 7 in which the reference numeral 45 designates arefrigeraliquefied. Liquefied refrigerant from the condenser 53 flowsthrough a capillary flow-impeding tube 54 to the evaporator 48, whereinit vaporizes to cool the same and the vapor thereafter repeats therefrigerating cycle. The compressor is driven by an electric motor 55which receives power from lines 56 and 51 through the thermostaticswitch 9 and lead 58. The thermostatic control 9 of this invention issecured by a metallic heat-conducting strip 59 to the evaporator 48 tocontrol its temperature and is connected in series with the line 56 andthe lead 58.

Operation The thermostatic'control 9 in the refrigerating cabinet 45operates as follows: Assume that the food compartment has beenrefrigerated to the proper temperature 'and that the bimetallic disc I2is in the upper position and the contacts 34, 36

i are separated as shown in Fig. 2. `A continuous heat leakage takesplaces through the walls o ally raises the vtemperatures of theevaporator 48 and disc I2. When the temperature of the disc I2 reaches apredetermined point it will snap downwardly and move contacts 34, 36 tothe closed position shown in Fig. l. The closing of the contacts 34, 36establishes an electrical ccnnection between lines-56 and 58 and startsthe operation of the refrigerating apparatus so that refrigerant issupplied to the evaporator 48.

The path of the current from one of the contacts 36 to the other contact36 is through the bimetallic strip 32 which strip is heated by thecurrent. The heating of the strip 32 tends to causeit to deect upwardlyat its center and this tendency manifests itself mainly as an upwardlydirected force on the actuating rod I5 and a downwardly directed forceon the contact buttons 34. During this time, the bimetallic disc I2 isbeing cooled by the evaporator 48 and its resistance to upward exing isthereby constantly decreased until the upwardly directed force of thebimetallic strip 32 on the actuating rod I5 overcomes both the deectingresistance of the disc and the pressure-of the spring I8 and causesthe'central portion of the disc I2 to snap upwardly. This upwardmovement occurs at a higher temperatre than would be the case if thestrip 32 did not exert an upwardly directed force. The upward movementof the disc I2 raises the operating rod I5, the bimetallic strip 32, andthe contacts 34 and interrupts the cur- `regulate refrigeratingapparatus and its installarent 4to the motor 55 and through the strip 32whereupon the refrigerating apparatus ceases to operate and the strip 32cools to its former temperature. The action of strip 32 thus decreasesthe temperature differential of the switch below that normally possessedby the disc I2 by increasing the temperature at which the contacts 36,31 are opened, while the temperature at' which said contacts 36, 31 areclosed is not affected. The temperature of the evaporator 48 istherefore controlled between narrow limits without sacrice in the sizeor in the ruggedness of construction of the thermostatic control switch9.

If it is desired to maintain a maximum degree of refrigeration such aswhen it is desired to freeze desserts or other comestibles in the evap-`orator 48, the adjusting screw 21 is turned downwardly to the positionshown in the dotted lines of Fig. 1. When thus screwed `downthebimetallic discy I2 and both contacts 34 are forced into the lowerposition, if not already in vsaid position, and the contacts 34 arelocked adjacent the contacts 3s so that the bimetaiic disc I2 ispowerless to open them. It will be obvious that in this position of theadjusting screw 21, the refrigerating apparatus will run continuously.

The contacts 34, 36 may also be locked in the open position which.position is utilizedwhen defrosting the evaporator 48 or forpermanently rendering the refrigerating apparatus 49, 53 inoperative.This is eiectedfby turning vthe adjusting screw 21 to the position shownby Fig. f

3. When moved into this position the upper edges 43 of the insulatingmaterial 39 engages the bimetallic strip 32 and causes it to flex at itssecurement to the actuating rod I5 and raise the extremities of thebimetallic strip 32 as the adjusting screw is turned down so that thecontacts 34 are raised from the contacts 36. When 1n this position, thebimetallic discA I2 is power.-

less to close the contacts 34, 36 and the refrigerating apparatusremains inoperative.

It will be apparent from the above description that this inventionprovides a thermostatic control switch adapted for 'use in refrigeratingapparatus which Vswitch has a small temperature diiierential and is ofsimple and rugged construction. The invention also provides means forlocking the contacts of the switch in either the open or the closedpositions.

While I have shown my invention in but one form, it will be obvious tothose skilled in the art that it is not so limited, but is susceptibleof various changes and modifications without departing from the spiritthereof, and I desire, therefore, that only such limitations shall beplaced thereupon as are specically set forth in the appended claims.

What I claim is:

1. In a thermostatic switch, the combination of electric contacts. asnap-acting, bimetallic element adapted to move selectively to twopositions in response to changes in temperature, means forinterconnecting said bimetallic element and said contacts to open thesame when said bimetallic element is in one of said positions and toclose said contacts when the bimetallic element is in the other of saidpositions, said interconnecting means including a second bimetallicelement adapted when heated to bias said snap-acting element toward thecontact-opening position, and means for heating said second bimetallicelement only when said contacts' are closed,

. when heated to bias said snap-acting response to changes intemperature, said means including a second bimetallic element adaptedbimetallic element toward the contact-opening position, and means forheating said last-named bimetallic element only when said contacts areclosed.

.5. In a thermostat, the combination of a bimetallic element adapted tosnap to one position when the temperature of the element decreases toa.v predetermined point and to snap to a second position when saidtemperature increases to `a second point above said predetermined point,

electric contacts. interconnecting means secured to said element and toone of said contacts to open said contacts when said element snaps tosaid one position and close said contacts when said element snaps tosaid second position, said interconnecting means including a ilexibleportion, a stop engageable by a part of said interconnecting means,'saidpart being located' between the ilexible portion and the contact securedto Athe interconnecting means, said stop being positioned for engagementby said interconnecting means when said interconnecting means is movedbeyond its contact-closing position, and means for selectively biasingsaid element toward and retaining the same in said second position, saidlast-named means also being adapted to move said element beyond saidsecond position to eiect engagement of said interconnesting means withsaid stop to open said contacts.

whereby the temperature diierential at which said mst-named bimetallicelement opens and closes said contacts is decreased.

2. In -a thermostat, the combination oi.' electrical contacts, meanseffective to open and close said contacts, a snap-acting bimetallicelement for actuating said means to fully open and fully close saidcontacts by selectively assuming contact-opening and contact-closingpositions in response to changes in temperature, said means including asecond bimetallic element adapted when heated to bias said snap-actingbimetallic element toward one of said positions, and means for heatingsaid second bimetallic element only when said snap-acting bimetallicelement is in the other of said Positions.

3. In a thermostat, the combination of electrical contacts, means foropening and closing said contacts, a snapacting bimetallic element foractuating said means by selectively assuming contact-opening andcontact-closing positions in response to changes in temperature, saidmeans including a second bimetallic element adapted when heated to biassaid snap-acting bimetallic element toward one of said positions, andmeans for heating said second bimetallic. elementonly when saidsnap-acting element is in the other of said positions. said secondbimetallic element being adaptedl for creep-type action.

4. In a thermostat, the combination of electrical contacts, means/foropening and closing said'contacts. a snap-acting bimetallic element foractuating saidmeans by selectively contact-opening and contactclosingpositions in 6. In a thermostatic switch, the combination of twoelectrical contacts at least one of which is movable, atemperature-responsive element, connecting means between saidtemperature-responsive element `and said movable contact to move saidmovable contact to open and closed positions with respect to the othercontact, said connecting means including a flexible portion, adjustablemeans including said connecting means for forcibly moving said movablecontact to one of said positions against the action of saidtemperature-responsive element, and a stop engaged by said connectinglmeans when said connecting means is moved beyond a position normallyeffective to move said movable contact to one of said positions, saidstop, when so engaged, deilecting the iiexible portion of saidconnecting means to move said movable contact to the other of saidpositions.

7. In a thermostatic switch, the combination of a iixed contact, atemperature-responsive eleadapted to be engaged by said member whenmoved to a predetermined position, said stop causing said exibleconnection to move said member to separate the movable contact from thehiredl contact 'when said member is moved beyond said predeterminedposition.

GERALD P. nancy.

